In our longitudinal study, veterans with penetrating head injuries received in World War II declined more in cognition from the 1950s to the 1980s than control veterans with peripheral nerve injuries. We now propose to examine some implications veterans with peripheral nerve injuries. We now propose to examine some implications of this precipitous decline observed in subjects with head injuries (HI). First, we will determine the generality of the effects of HI on behavior by continuing our longitudinal study of 203 surviving veterans of the Korean Conflict. Retesting the Korean Conflict veterans will permit us to determine (a) whether control relative to uninjured penetrating HI increased cognitive decline in that sample penetrating and closed HI our previous findings: whether subjects, replicating decline equally: and (c) which of a variety of cognitive, sensory, sensorimotor, and psychiatric measures showed precipitous decline following HI. The second question concerns the pathophysiology of precipitous decline. We will enter the surviving Korean Conflict veterans into a new longitudinal protocol. Morphometric analyses of magnetic resonance (MR) images will determine the volumes of lesions and of selected brain structures, and a series of cognitive, sensory, and motor tests and psychiatric instruments will assess behavioral functions. Future grant applications will seek additional funding as necessary to repeat testing and morphometry at successive 5-year intervals. Correlations between morphometric and behavioral changes will provide evidence regarding the neural substrate of the effects of HI upon behavioral decline. We believe that two degenerative processes contribute to precipitous decline, and that morphometric analysis is sensitive to the effects of both: (a) transneuronal degeneration consequent to the original injury that compromises new brain regions: and (b) brain atrophy due to aging that impairs the ability of regions spared by the original injury to compensate for damaged tissue. The third question integrates our laboratory's long-standing interests in the behavioral effects of brain injury and of Alzheimer's disease (AD). Administering neurologic examinations and a small number of cognitive tests to the 212 surviving World War II veterans will permit us to determine (a) whether prior HI is a risk factor for AD and (b) whether the precipitous cognitive decline that follows HI progresses to dementia.